Thousands of terminally-ill patients will be denied life-extending treatment because the government's drugs regulator says it is "not cost effective".

Cancer researchers and charities have reacted angrily after the National Institute for Health and Care Excellence (Nice) decided men with prostate cancer should not be given abiraterone until after chemotherapy.

Prostate Cancer UK said it was a "kick in the teeth" for patients who would be denied extra time with their loved ones.

Owen Sharp, chief executive of the charity, said: "It's a fiasco. For many this presented a vital opportunity for extra time with loved ones and a chance to delay chemotherapy and the debilitating side effects which come with it.

"This is just the latest in a string of hugely disappointing rulings on prostate cancer drugs.

"The current system is flawed - it is not fit for purpose."

Prostate cancer is the most common cancer among British men, with 40,000 cases every year.

However, Nice said abiraterone was "not cost effective at its current price".

It costs almost £3,000 a month - although the NHS had negotiated discounts.

Image:Researchers say abiraterone can aid 'longer, healthier lives'

Nice ruled it should not be widely used in the NHS in England to treat pre-chemotherapy patients whose cancer had spread and who had already received another type of hormone therapy.

But experts from The Institute of Cancer Research (ICR) said there was clear evidence abiraterone was beneficial before chemotherapy.

Professor Paul Workman said: "Men will have to wait until they are in the final stage of their lives before they can access this treatment, and men who are too frail to receive chemotherapy face not being able to receive abiraterone at all."

Abiraterone, which is also known as Zytiga, is a four-a-day pill made by drugs company Janssen.

Nice's chief executive Sir Andrew Dillon said: "We know how important it is for patients to have the option to delay chemotherapy and its associated side effects, so we are disappointed not to be able to recommend abiraterone for use in this way.

"However, the manufacturer's own economic model demonstrated that the drug does not offer enough benefit to justify its price."

Janssen medical director Dr Peter Barnes said: "We are very disappointed with this decision which, if it stands, will leave thousands of men in England in the advanced stages of prostate cancer with no option but to accept chemotherapy - which they may not necessarily need or want yet - before being eligible to receive abiraterone routinely on the NHS."

Patients will now have to rely on the Cancer Drugs Fund, a pot set aside for cancer drugs not routinely available on the NHS.